1. Field of the Invention
The present invention relates to a Fe-based amorphous alloy applied, for example, to a powder core of a transformer, a power supply choke coil, or the like and a coil encapsulated powder core.
2. Description of the Related Art
Concomitant with recent trend toward a higher frequency and a larger current, a powder core and a coil encapsulated powder core, which are applied to electronic components and the like, are each required to have superior direct-current superposing characteristics, a low core loss, and a constant inductance in a frequency range up to MHz.
Incidentally, a heat treatment is performed on a powder core formed to have a targeted shape from an Fe-based amorphous alloy with a binding agent in order to reduce stress deformation generated when a powder of the Fe-based amorphous alloy is formed and/or stress deformation generated when the powder core is formed.
However, in consideration of the heat resistance of a coated lead wire, a binding agent, and the like, a temperature T1 of the heat treatment actually applied to a core molded body could not be increased to an optimum heat treatment temperature at which the stress deformation of the Fe-based amorphous alloy was effectively reduced, and the core loss could be minimized.
Accordingly, in the past, the optimum heat treatment temperature was high, (the optimum heat treatment temperature−the heat treatment temperature T1) was increased, the stress deformation of the Fe-based amorphous alloy could not be sufficiently reduced; hence, the characteristics thereof could not be fully utilized, and the core loss could not be sufficiently reduced.
Therefore, in order to decrease the optimum heat treatment temperature as compared to that in the past and to improve the core characteristics, a glass transition temperature (Tg) of the Fe-based amorphous alloy was necessarily decreased. In addition, at the same time, in order to improve amorphous formability, a conversion vitrification temperature (Tg/Tm) was necessarily increased, and furthermore, in order to improve the core characteristics, it was necessary to increase magnetization and to improve corrosion resistance.
The inventions disclosed in Japanese Unexamined Patent Application Publication Nos. 2008-169466, 2005-307291, 2004-156134, 2002-226956, 2002-151317, 57-185957, and 63-117406 all have not aimed to satisfy all of a low glass transition temperature (Tg), a high conversion vitrification temperature (Tg/Tm), and good magnetization and corrosion resistance, and hence, addition amounts of individual elements were not adjusted to satisfy the properties as described above.